Powder composition of polyarylene ether ketone ketones allowing an excellent castability/coalescence balance suitable for laser sintering

ABSTRACT

A powder composition of polyarylene ether ketone ketones allowing an excellent castability/coalescence balance suitable for laser sintering. The present invention concerns a composition comprising between 99.6 and 99.99% by weight of at least one powder of at least one polyarylene ether ketone and 0.01 to 0.4% by weight of a hydrophilic flow agent. This hydrophilic flow agent is characterised by an increase in mass (quantity of water absorbed) of more than 0.5% after 5 days of conditioning at a relative humidity of 95%. This increase in mass of the flow agent is determined by means of a Karl Fischer measurement after desorption of the water by a 5-minute treatment at 170° C. This composition is suitable for laser sintering. In particular, it gives the powder an excellent castability/coalescence balance.

The present invention relates to a composition comprising from 99.6% to 99.99% by weight of at least one powder of at least one polyarylene ether ketone and 0.01% to 0.4% by weight of a hydrophilic flow agent. This hydrophilic flow agent is characterized by a gain in mass (amount of water absorbed), after 5 days of conditioning at a relative humidity of 95%, of greater than 0.5%. This gain in mass of the flow agent is determined by Karl Fischer measurement after desorption of the water via a 15-minute treatment at 170° C. This composition is suitable for laser sintering. It in particular allows an excellent castability/coalescence compromise for the powder.

Polyarylene ether ketones and more particularly polyether ketone ketones (PEKK) are highly efficient materials. They are used for applications with temperature constraints and/or mechanical or even chemical constraints. These polymers are found in fields as varied as aeronautics, offshore drilling and medical implants. They may be used by molding, extrusion, compression, spinning or laser sintering, especially. However, their use in the latter process requires powder preparation conditions that ensure good flowability allowing implementation in the laser sintering process as described below.

The technology of powder sintering under a laser beam serves to manufacture objects in three dimensions such as prototypes and models, but also functional parts, especially in the motor vehicle, nautical, aeronautic, aerospace, medical (prostheses, auditive systems, cell tissues, etc.), textile, clothing, fashion and decorative fields, casings for electronics, telephony, home automation, information technology and lighting.

A thin layer of powder is deposited on a horizontal plate maintained in a chamber heated to a certain temperature. The laser supplies the energy required to sinter the powder particles at various points in the layer of powder in a geometry corresponding to the object, for example with the aid of a computer having the shape of the object in its memory and rendering this shape in the form of slices. Next, the horizontal plate is lowered by a value corresponding to the thickness of a layer of powder (for example between 0.05 and 2 mm and generally about 0.1 mm) and a new layer of powder is then deposited. The laser supplies the energy required to sinter the powder particles in a geometry corresponding to this new slice of the object, and so on. The procedure is repeated until the entire object has been manufactured.

In this process of powder sintering under a laser beam, it is imperative to have available powders that have good flowability, which allows good layering of said powders. Moreover, good coalescence of the powder is necessary after melting induced by the laser, so that the mechanical properties of the manufactured objects are maximized.

Powders are thus sought which have, firstly, good flowability and, secondly, good coalescence during the sintering process.

In the field of laser sintering, it is common practice to add flow agents to improve the flowability of powders.

US 2004/0 204 531 describes the advantage in polyamide of hydrophobic silicas versus hydrophilic silicas. Specifically, the flowability is deteriorated after moisture uptake in the case of using hydrophilic silicas, whereas it is unchanged in the case of using hydrophobic silicas.

In the field of polyarylene ether ketones (PAEK), the flowability is known to be improved by using a suitable heat treatment.

U.S. Pat. No. 7,847,057 relates to a process for the heat treatment of polyarylene ether ketone powders, which consists in exposing the powder to a heat treatment for over 30 minutes at a temperature 20° C. above the glass transition temperature of the polymer.

This treatment applied to polyether ether ketones (PEEK) makes it possible to obtain powders whose flowability is acceptable for the laser sintering process. The coalescence aspect is not discussed in said patent, and in particular no example demonstrates that the coalescence is effective, modified or even improved by the heat treatment.

WO 2012/047 613 also describes a heat treatment applied more particularly to polyether ketone ketone (PEKK) powders, which consists in exposing the powder to a heat treatment for several hours between the transition temperatures of the various crystalline phases, more particularly by approaching the melting point of the polymer, corresponding to the crystalline form having transition at the highest temperature. The flowability of the powder is thereby improved and the crystallinity resulting from this treatment is conserved during the sintering process, giving the sintered object certain advantageous physical properties, but appearing insufficient for certain applications. The coalescence aspect is not discussed in said patent, and in particular no example demonstrates that the coalescence is effective, modified or even improved by the heat treatment.

To satisfy the requirements of having available powders with good flowability and good coalescence, the Applicant conducted a series of tests demonstrating that, for polyarylene ether ketones, the addition of a hydrophilic flow agent firstly allows good flowability, and secondly that this flowability is conserved even after residence in a humid atmosphere. The latter result appears unexpected and very surprising with regard to the prior art (US 2004/0 204 531).

In addition, the Applicant found that, for such compositions, the coalescence of these polyarylene ether ketone powders supplemented with hydrophilic flow agent is superior to that of polyarylene ether ketone powders supplemented with hydrophobic flow agent.

SUMMARY OF THE INVENTION

The invention relates to a composition comprising from 99.6% to 99.99% by weight of at least one powder of at least one polyarylene ether ketone and 0.01% to 0.4% by weight of a hydrophilic flow agent, preferably from 0.01% to 0.2% by weight of a hydrophilic flow agent and, more particularly, preferably from 0.01% to 0.1% by weight of a hydrophilic flow agent. This hydrophilic flow agent is characterized by a gain in mass (amount of water absorbed), after 5 days of conditioning at a relative humidity of 95%, of greater than 0.5%, preferably greater than 0.8%. This gain in mass of the flow agent is determined by Karl Fischer measurement after desorption of the water by a 15-minute treatment at 170° C.

The invention also relates to the use of the compositions of the invention and also to the objects manufactured with the aid of these compositions, in particular with the aid of a laser sintering process.

DETAILED DESCRIPTION

The polyarylene ether ketones (PAEK) used in the invention comprise units having the following formulae:

(—Ar—X—) and (—Ar₁—Y—)

in which: Ar and Ar₁ each denote a divalent aromatic radical; a minor proportion (<10%) of these units may be replaced with radicals with a valency of greater than 2 to introduce branches. Ar and Ar₁ may preferably be chosen from 1,3-phenylene, 1,4-phenylene, 4,4′-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene; X denotes an electron-withdrawing group; it may preferably be chosen from the carbonyl group and the sulfonyl group, Y denotes a group chosen from an oxygen atom, a sulfur atom, an alkylene group, such as —CH₂— and isopropylidene.

In these units X and Y, at least 50%, preferably at least 70% and more particularly at least 80% of the groups X are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least 80% of the groups Y represent an oxygen atom.

According to a preferred embodiment, 100% of the groups X denote a carbonyl group and 100% of the groups Y represent an oxygen atom.

More preferentially, the polyarylene ether ketone (PAEK) may be chosen from:

-   -   a polyether ether ketone, also known as PEEK, comprising units         of formula I:

The sequences may be totally para (Formula I), but it would not constitute a departure from the context of the invention to introduce, partially or totally, meta sequences. Two examples (nonlimiting list) are given below:

-   -   a polyether ketone, also known as PEK, comprising units of         formula II:

Similarly, the sequences may be totally para (Formula II), but it would not constitute a departure from the context of the invention to introduce, partially or totally, meta sequences:

-   -   a polyether ketone ketone, also known as PEKK, comprising units         of formula IIIA, of formula IIIB and a mixture thereof:

-   -   and a polyether ether ketone ketone, also known as PEEKK,         comprising units of formula IV:

Similarly, meta sequences may be introduced into this structure without departing from the invention.

Other arrangements of the carbonyl group and of the oxygen atom are also possible. It would therefore not constitute a departure from the context of the invention to use them.

It is also possible to incorporate into the structure a divalent radical of the phthalazinone type having the following formula:

The polyarylene ether ketone that may be used according to the invention may be semicrystalline or amorphous. Preferably, the polyarylene ether ketones are polyether ketone ketones comprising a mixture of units IIIA and IIIB such that the mass percentage of terephthalic units relative to the sum of the terephthalic and isophthalic units is between 55% and 85% and preferably between 55% and 70%, ideally 60%. The terms “terephthalic unit” and “isophthalic unit” mean the formula of terephthalic acid and isophthalic acid, respectively.

These polyarylene ether ketones are in the form of powders that may be prepared by grinding or precipitation.

Mixtures of various polyarylene ether ketone powders are not excluded in the context of the invention. According to a preference, the mixtures of various polyarylene ether ketone powders comprise a polyether ketone ketone combined with another polyarylene ether ketone or a mixture of two PEKKs of different chemical structure. Thus, a polyarylene ether ketone will be combined with a PEK, PEEKEK, PEEK, PEKEKK or PEKK. According to a preferred form, the PEKK will be combined with PEK, PEEKEK, PEEK or PEKEKK or a PEKK of different chemical formula, the PEKK representing more than 50% by mass, limit inclusive.

The hydrophilic flow agents used in the context of the invention may be inorganic pigments preferably chosen from silicas and aluminas.

The hydrophilic silicas used in the context of the invention are constituted of silicon oxide. They are fumed silicas without any specific treatment, unlike the hydrophobic silicas, which are fumed silicas that have undergone a chemical treatment such as grafting with dimethylchlorosilane. It would not constitute a departure from the context of the invention to use silicas synthesized via another manufacturing method.

The silicas commonly used are commercial products whose trade name is Aerosil® (supplied by Evonik) or Cab-O-Sil® (supplied by Cabot).

These silicas are composed of nanometric primary particles (typically between 5 and 50 nm for fumed silicas). These primary particles are combined to form aggregates. In use as flow agent, silicas are found in various forms (elementary particles and aggregates).

The powders or powder mixtures comprising hydrophilic flow agents used in the context of the invention may, where appropriate, be supplemented or contain various compounds. Among these compounds, mention is made of reinforcing fillers, especially mineral fillers such as carbon black, nanotubes, which may or may not be carbon-based, fibers (glass, carbon, etc. fibers), which may or may not be ground, stabilizers (light stabilizers, in particular UV stabilizers, and heat stabilizers), optical brighteners, colorants, pigments, energy-absorbing additives (including UV absorbers) or a combination of these fillers or additives.

EXAMPLES Measurement of the Flowability

The flowability of these powders was determined in glass funnels in the following manner:

-   -   Fill glass funnels with a 17 or 12 mm orifice (FIG. 1) with the         powder up to 5 mm from the rim. Stopper the bottom orifice with         the finger.

With, for a 12 mm funnel:

d_(e)=39.2 mm d_(o)=12 mm h=106 mm h₁=83 mm and for a 17 mm funnel: d_(e)=42.0 mm d_(o)=17 mm h=112 mm h₁=67 mm

-   -   Measure with a chronometer the flow time of the powder.     -   If flow does not take place, tap the funnel using a spatula.         Repeat the operation if necessary.     -   Note the flow time and the number of taps given with the         spatula.

Estimation of the Coalescence:

The coalescence of the powders is estimated by means of the following protocol:

-   -   deposition of powder onto a steel plate     -   baking, at 340° C. for 15 minutes, of the plate coated with         powder     -   observation of the coated plate after cooling after removal from         the oven

The coalescence will be judged to be proportionately better the more invisible the steel plate has become following the coalescence/film formation of the powder.

Example 1

A Kepstan® 6003 PL powder from the company Arkema, containing 60% of terephthalic units relative to the sum of the terephthalic and isophthalic units, whose particle size has a Dv50 of 50 μm plus or minus 5 μm, was supplemented with 0.4% of Cab-O-Sil® TS-610 silica in a Magimix kitchen blender at high speed for 100 seconds.

The Dv50 is also known as the volume median diameter, which corresponds to the particle size value which divides the population of particles examined exactly into two. The Dv50 is measured according to standard ISO 9276—parts 1 to 6. In the present description, a Malvern Mastersizer 2000 particle size analyzer is used, and the measurement is taken in the liquid route by laser diffraction on the powder.

The silica Cab-O-Sil® TS-610 is a fumed silica that has been made hydrophobic by treatment with dimethylchlorosilane. It will be referred to hereinbelow as “TS-610”.

The powder has excellent flowability (time <10 s, 0 taps for a 17 mm funnel), but the coalescence, estimated as described above, is very poor, the steel plate still being clearly visible.

The silica may thus be an anti-coalescer at a high content.

Example 2

A Kepstan® 6003 PL powder from the company Arkema, containing 60% of terephthalic units relative to the sum of the terephthalic and isophthalic units, whose particle size has a Dv50 of 50 μm plus or minus 5 μm, was supplemented with Cab-O-Sil® TS-610 silica in a Magimix kitchen blender at high speed for 100 seconds.

A second sample of the same Kepstan powder is supplemented with Cab-O-Sil® M-5 silica according to the same protocol. The silica Cab-O-Sil® M-5 is a hydrophilic fumed silica that has not undergone any specific treatment. It will be referred to hereinbelow as “M-5”.

The flowability results for the two supplemented powders are given in Table 1 in comparison with the silica-free powder.

TABLE 1 0.2% Without 0.1% TS TS 0.1% 0.2% silica 610 610 M5 M5 Flowability Time (s) 90 60 12 80 22 12 mm funnel Number of multi multi 3 multi 14 taps Flowability Time (s) 48 13 9 22 12 17 mm funnel Number of 40  3 0 10 1 taps

The term “multi” is used when the funnel is tapped continuously.

It is found that the two types of silica improve the flowability and they are thus both potential flow agents for PEKK.

Example 3

Another Kepstan® 6003 PL powder from the company Arkema is supplemented in the Magimix blender either with 0.05% Cab-O-Sil® TS-610 silica or with 0.05% Cab-O-Sil® M-5 silica.

These powders are, on the one hand, stored at 23° C. and 50% relative humidity up to moisture saturation (in the case, for example, of storage of the powder before machine use). The moisture content is measured by the Karl Fischer method (desorption of water from the Kepstan® powder by treatment for 20 minutes at 250° C.). On the other hand, the powders are dried overnight at 140° C. The moisture content is also measured by the Karl Fischer method (same protocol as above).

The flowability results for the two supplemented powders with different moisture contents are given in Table 2.

TABLE 2 0.05% TS 610 0.05% M5 Moisture content 0.25% 0.5% 0.25% 0.53% Flowability Time (s) 7 5 6 6 17 mm Number 0 0 0 0 funnel of taps

The moisture contents of 0.5% and 0.53% correspond to the state of the material saturated with moisture at 23° C. and 50% relative humidity.

The moisture contents of 0.25% correspond to the state of the material after drying at 140° C. overnight.

The moisture contents are not affected by the nature of the silica.

It emerges that, irrespective of the silica used, the flowability is not affected by the moisture content. In particular, no deterioration of the flowability is observed for powders saturated with moisture (23° C., 50% relative humidity), even in the case of using a hydrophilic silica as flow agent.

Example 4

Three samples of Example 2 (not supplemented, supplemented with 0.2% of hydrophobic silica (TS-610), supplemented with 0.2% of hydrophilic silica (M-5)) are deposited on three steel plates.

These coated plates are placed in an oven maintained at 340° C. for 15 minutes.

They are then cooled, and the PEKK coating at the surface of the plates is then observed (FIGS. 2 and 3), visually and under binoculars (Stemi SV11 from Zeiss).

Visually (FIG. 2), a much smoother surface is observed when the hydrophilic silica (M-5) is used, demonstrating the good coalescence of the powder during the oven treatment. Without silica and with the TS-610 silica, the coating is not continuous and, consequently, the steel plate remains locally visible.

The binocular images (FIG. 3) confirm the preceding observations: there are areas where locally the steel plate can still be seen in the case of the non-supplemented powder and of the powder supplemented with 0.2% of TS-610 silica, whereas, in the case of the powder supplemented with M-5 silica, the steel plate is no longer visible. This confirms the better coalescence of the powder supplemented with M-5 during the oven treatment. 

1. A composition comprising from 99.6% to 99.99% by weight of at least one powder of at least one polyarylene ether ketone and 0.01% to 0.4% by weight of a hydrophilic flow agent, said hydrophilic flow agent being characterized by a gain in mass (amount of water absorbed), after 5 days of conditioning at a relative humidity of 95%, of greater than 0.5%, said gain in mass of the flow agent being determined by Karl Fischer measurement after desorption of the water by a 15-minute treatment at 170° C.
 2. The composition as claimed in claim 1, in which the hydrophilic flow agent is a hydrophilic silica.
 3. The composition as claimed in claim 1, in which at least one polyarylene ether ketone is PEKK.
 4. The composition as claimed in claim 3, in which the PEKK has a mass percentage of terephthalic units relative to the sum of the terephthalic and isophthalic units of between 55% and 85%.
 5. The composition as claimed in claim 3, in which, in addition to the PEKK, a PEK, PEEKEK, PEEK, PEKEKK or PEKK powder of different chemical structure is added, the PEKK representing more than 50% by mass, limit inclusive.
 6. The composition as claimed in claim 1, containing a filler.
 7. The composition as claimed in claim 1, containing at least one additive.
 8. The use of a composition as claimed in claim 1 in a laser sintering process.
 9. An object obtained using a composition as claimed in claim
 1. 